A secondary battery is a device that stores electrical energy in chemical form and converts the stored chemical energy into electrical energy to generate electricity when needed. The secondary battery is also referred to as a rechargeable battery because it can be recharged repeatedly. A common secondary battery includes a lead accumulator, a NiCd battery, a NiMH accumulator, a Li-ion battery, a Li-ion polymer battery, and the like. When compared to a disposable primary battery, not only is the secondary battery more economically efficient, it is also more environmentally friendly.
A secondary battery is currently used in applications requiring low electric power, for example, equipment to start a vehicle, a mobile device, a tool, an uninterruptible power supply, and the like. Recently, as the development of wireless communication technologies has been leading to the popularization of mobile devices and even to the mobilization of many kinds of conventional devices, the demand for a secondary battery has been dramatically increasing. A secondary battery is also used in an environmentally friendly next-generation vehicle such as a hybrid vehicle or an electric vehicle to reduce the cost and weight and to increase the service life of the vehicle.
Generally, most secondary batteries have a cylindrical, prismatic, or pouch shape. This is associated with a fabrication process of a secondary battery that mounts an electrode assembly composed of an anode, a cathode, and a separator in a cylindrical or prismatic metal casing or a pouch-shaped casing of an aluminum laminate sheet, and injects an electrolyte into the electrode assembly. Because a predetermined mounting space for the electrode assembly is necessary in this process, the cylindrical, prismatic or pouch shape of the secondary battery is a limitation in developing various shapes of mobile devices. Accordingly, there is a need for a new type of secondary battery that is easily adaptable in shape.
To fulfill this need, suggestions have been made to develop a linear battery having a very high ratio of length to cross-sectional diameter. Korean Patent Application publication No. 2005-99903 discloses an adaptable battery consisting of an inner electrode, an outer electrode and an electrolyte layer interposed therebetween. However, such battery has poor flexibility. The linear battery uses a polymer electrolyte to form an electrolyte layer, but this causes difficulties in the inflow of the electrolyte into an electrode active material, thereby increasing the resistance of the battery and deteriorating the capacity and cycle characteristics thereof.